Mr Thayne spoke out after his interim replacement as chief executive also quit.

Dr Anton van Dellen returned to work in the Staffordshire service.

But Mr Thayne who quit in May after less than three months said: "The great problem I found, and then Anton van Dellen found, to make those changes you have got to get the staff to change, to work in a way that matches patient demand.

"You have to realise in Wales the trade unions are very powerful and they don't talk to chief executives, they talk to ministers."

But unions claimed Mr Thayne ignored staff and unions when he was in temporary charge.

Tony Chatfield from Unison said: "The staff really understand that it cannot continue the way it is. It needs modernisation."